Hybrid electric propulsion system using a dual shaft turbine engine

ABSTRACT

An electric propulsion system for a vehicle having an electric drive motor. A generator supplies electric current to the motor. A dual shaft turbine engine having a compressor and a gasifier coupled with a first shaft and a power turbine, flywheel and generator coupled to a second shaft provide electric current to the electric drive motor. The first and second drive shafts are uncoupled and are allowed to spin independently of one another. Exhaust gases from the gasifier turn the power turbine, thus the turning power turbine turns the generator and flywheel as a unit.

RELATED APPLICATIONS

This application is a continuation of application Ser. No. 08/551,261,filed Oct. 31, 1995, now U.S. Pat. No. 5,762,156, and Ser. No.08/551,262, now U.S. Pat. No. 5,584,174 titled: POWER TURBINE FLYWHEELASSEMBLY FOR A DUAL SHAFT TURBINE ENGINE, filed Oct. 31, 1995, namingBates, Belaire, Stephan as inventors, and incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hybrid propulsion system for avehicle using a turbine engine. More specifically, the present inventionrelates to the use of a dual shaft turbine engine having a flywheeldirectly coupled to the second shaft of the engine and uncoupled fromthe first shaft of the engine.

2. Description of the Related Art

Liquid fueled turbine engines have been used to power vehicles becauseof their operating efficiency and durability. They are especially usefulwhen used at a constant speed and under a constant vehicle load.Operating a turbine engine at a constant speed and load greatly extendsthe durability of the engine and optimizes its fuel efficiency. Turbineengines may be directly coupled to the vehicle drive wheels to provide amechanical drive or, alternatively, they maybe used to operate agenerator to provide electric drive.

It is known to use a turbine engine to directly power the drive wheelsof a vehicle as illustrated in U.S. Pat. No. 4,157,011, issued Jun. 5,1979, to Liddle. The Liddle patent teaches the use of a single shaftturbine engine mechanically coupled through a continuously variabletransmission to the vehicle drive wheels. The engine is used in anintermittent fashion and requires repeated restarts. A flywheel locatedbetween the turbine and the transmission provides a rotational inertiathat is sufficient to start turbine engine. An optional clutch allowsthe turbine engine to be switched on and off. The vehicle may bemanually driven for a short period of time on the inertia of theflywheel once the turbine engine is shut down. The primary disadvantagesof this system are the limitations of continuously variabletransmissions to transmit mechanical energy. Heavy vehicle loadrequirements, such as the torque needed to power the vehicle up hills orover obstacles, are transmitted through the transmission and to theturbine engine. This creates a load or drag on the engine and therebyreduces the engine's operating efficiency. Additionally, frictionalforces within the continuously variable transmission significantlyreduce the operating efficiency of the propulsion system. These andother disadvantages of mechanically coupling the engine to the drivewheels has led others to indirectly couple the turbine engine to thevehicle wheels.

To maintain the efficiency of a turbine engine, it has been used topower a generator. The generator in turn powers a vehicle traction motorthat operates the drive wheels. A system that used this approach isillustrated in U.S. Pat. No. 4,336,856, issued Jun. 29, 1982, to Gamell.Like the Liddle patent, the Gamell patent teaches a single shaft turbineengine directly coupled to a generator/motor. The generator/motor inturn provides electrical current to power a vehicle traction motor. Themotor drives the vehicle wheels.

A flywheel attached adjacent the drag turbine provides additionalrotational inertia to the turbine engine. Single shaft turbine engines,as the type used in Gamell, suffer from the problem of transmittingvehicle drag to the turbine engine when the vehicle is under asignificant load. This drag causes an increased torque on the turbineengine, thereby reducing the engine operating efficiency.

The flywheel taught by Gamell exposes the rotating, flywheel to ambientair. The air drag on the rotating flywheel reduces the flywheelefficiency and thus, the overall efficiency of the vehicle. Others haveused flywheels contained within a vacuum enclosure to reduce the airdrag on the flywheel. These systems have required gearing to match theflywheel rotational speed to that of the engine.

It is desirable to provide a turbine powered hybrid vehicle whichdecouples the turbine engine from the driven wheels. It is furtherdesirable to combine a flywheel with the turbine engine to provideadditional torque when the vehicle is under load or to provide a purelyelectric drive to the vehicle without the use of the turbine engine. Itis also desired to provide a hybrid electric power train for a vehiclethat permits the use of sealed flywheel within a vacuum enclosure. It isfurther desirable to provide a flywheel system that rotates directlywith the output of the vehicle engine while contained within a vacuumenclosure. These and other advantages and features of the presentinvention would be more fully described below and in the accompanyingdrawings.

SUMMARY OF THE INVENTION

The present invention provides electric propulsion system for a vehiclehaving an electric drive motor. A generator supplies electric current tothe motor. A dual shaft turbine engine having a compressor and agasifier coupled with a first shaft, and a power turbine, flywheel andgenerator coupled to a second shaft provide electric current to theelectric drive motor. The first and second drive shafts are uncoupledand are allowed to spin independently of one another. Exhaust gases fromthe gasifier turn the power turbine; thus the turning power turbineturns the generator and flywheel as a unit.

The electric drive motor may also be operated in a generator mode toprovide regenerative braking in the vehicle. The generator may be usedas a motor to accept regenerative braking energy from themotor/generator in the form of electric current to store that energy asrotational energy within the flywheel. The dual shaft turbine designpermits the use of an uncoupled power turbine so that load or torquetransmitted or demanded by the drive wheels is not directly presented tothe first shaft of the turbine engine. Thus, the first shaft turns at arelatively constant velocity and the turbine engine maintains an overallhigh energy efficiency. The dual shaft design also permits the use of aflywheel directly coupled to the power turbine without the need of aclutch or transmission. This construction greatly simplifies startingthe engine because the relatively heavier flywheel and generator/motorneed not turn in tandem with the compressor and gasifier.

In an alternative embodiment of the present invention, the flywheel isenclosed within a sealed vacuum chamber so as to reduce the frictionalloses in operating the flywheel. The flywheel is directly coupled to thesecond drive shaft by means of a magnetic coupling.

In yet another alternative embodiment of the present invention, theflywheel is integrated between blades of a power turbine to eliminatethe need for a magnetic coupling and sealed vacuum chamber. Thisembodiment is believed to provide many of the drag reducing efficienciesof operating the flywheel in a vacuum environment without thecomplexities of the vacuum enclosure.

The use of an uncoupled second shaft permits the gasifier turbine to bestarted freely without load and operate independently of any loaddemanded by the drive wheels. Neither high speed clutches nortransmissions are needed because the power turbine is propelled byexhaust gases emitted from the gasifier turbine.

These and other objects and advantages of the present invention willbecome more apparent to those skilled in the art from the followingdescription and reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of a hybrid electric propulsion systemusing a vacuum containment chamber.

FIG. 1a is a diagrammatic view of an alternative embodiment of themagnetic coupling shown in FIG. 1.

FIG. 2 is yet another alternative embodiment of the present inventionwithout the vacuum containment chamber.

FIG. 3 is still further another alternative embodiment of the presentinvention combining the flywheel between blades of the power turbine.

FIG. 4 is a cross-sectional view of the power turbine/flywheelillustrated in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A schematic representation of the present invention is illustrated inFIG. 1. The hybrid electric vehicle propulsion system 10 includes a twinshaft turbine engine 12. The engine 12 includes a first shaft 14. acompressor turbine 16 and a gasifier turbine 18. The compressor turbine16 receives ambient air from an air inlet 20. The compressed air passesthrough a heat exchanger 22. Fuel is added to the compressed air by acombuster 24. The air/fuel mixture coming from combuster 24 is ignitedand directed to the gasifier turbine 18. The combustion byproducts fromgasifier turbine 18 greatly expand in the form of high velocity exhaustgases. These gasses are directed from gasifier turbine 18 to a powerturbine 26. The power turbine 26 is connected to a second shaft 28. Thefirst shaft 14 and the second shaft 28 together form the dual shaftturbine engine 12. The exhaust gases cause power turbine 26 and thesecond shaft 28 to spin rapidly. Exhaust gases passing through powerturbine 26 are directed to the heat exchanger 22 and exhausted. Dualshaft turbines that operate in this fashion are well known and have beenused commercially in aircraft applications.

The rotary output of engine 12 is directly coupled through the secondshaft 28 to a generator/motor 30. The generator/motor 30 is designed tooperate at the engine speeds of turbine engine 12. The rotation of thesecond shaft 28 causes the rotor (not shown) within the generator/motor30 to turn and thereby create an AC electric current. Generator/motor 30is designed to provide most of the electric current needed to drive ahybrid electric vehicle.

As will be more fully described below, the generator/motor 30 is alsooperable as a motor so as to receive electric current and rotate aflywheel. The generator/motor 30 is connected to an inverter/powercontroller 32. Inverter/power controller 32 converts the AC electriccurrent coming from the generator/motor 30 into DC electric current.Many electric vehicles use DC current to operate DC drive motors or asan interim before being reconverted to AC to operate an AC drive motor.Inverter/power controller 32 also limits the amount of current thatpasses to or from generator/motor 30 to prevent the electric currentfrom exceeding the capacities of the motor/generator 30.

The inverter/power controller 32 provides electric current to electricdrive motor/generator 34. The electric drive motor/generator 34 isdirectly coupled to the vehicle wheels 36 and provides the tractiveforce necessary to propel the vehicle. The drive motor/generator 34 maybe either AC or DC. If drive motor 34 is AC, an additional inverter (notshown) is necessary to receive the DC current from inverter/powercontroller 32. The electric drive motor 34 is preferably also operableas a generator to provided regenerative breaking for the vehicle. Whendrive motor/generator 34 is operating as a generator, rotational energyfrom the vehicle drive wheels 36 causes the drive motor/generator 34 tocreate an AC current and slow the vehicle. The regenerative electriccurrent passes through the inverter/power controller 32 to thegenerator/motor 30. The generator/motor 30 is caused to operate as amotor and rotates the second shaft 28. Electric current from drivemotor/generator 34 is stored as rotational energy. The inverter/powercontroller 32 coordinates the operation of the drive motor/generator 34and the generator/motor 30. The excess rotational energy in the secondshaft 28 may be stored within a high-speed flywheel assembly 38.

The flywheel assembly 38 is magnetically coupled to the second shaft 28by means of a magnetic coupling 42. The flywheel assembly 38 is directlycoupled to second shaft 28 by means of a magnetic coupling 42. Themagnetic coupling 42 comprises a magnetic spindle 44 that is attached tothe second shaft 28. A magnetic rotor 46 is attached to the flywheel 40and overlies the spindle 44. Commercially available magnetic couplingsare capable of transmitting the torque from the second shaft 28 to theflywheel 40. The magnetic coupling 42 provides a direct rotationalcoupling between the second shaft 28 and the flywheel 40, that is, everyrevolution in the second shaft 28 causes a revolution in the flywheel40. The magnetic coupling 42 is used so that a vacuum containment vessel48 may be placed completely around the flywheel 40. The air within thevessel 48 is evacuated to reduce the air resistance and drag on theflywheel 40. This reduced drag increases the efficiency of the flywheel40 when compared to flywheels operating in ambient air. Commerciallyavailable co-axial couplings are manufactured by Dexter MagneticMaterials Division, Sylvania, Ohio.

An alternative to the spindle/rotor magnetic coupling 42 illustrated inFIG. 1, is a plate-type magnetic coupling illustrated in FIG. 1a. Aplate-type magnetic coupling 42' comprises two opposing plates 43, 45,each having a permanent dipole magnet. Opposite poles of the magnets inplates 43, 45 (not shown) cause plate 43 to magnetically couple to plate45 and directly rotate flywheel 40. The plate-type magnetic couplingincludes a barrier which mounts with a flange (not shown) surrounding ahole in the vacuum housing. Plate-type magnetic couplings arecommercially available and exemplary couplings include thosemanufactured by Dexter Magnetic Materials Division, Sylvania, Ohio.

Plate-type magnetic couplings are less complex and lower in cost incomparison to spindle/rotor-type magnetic couplings. However, plate-typemagnetic couplings are attracted to one another. The bearings supportingthe second shaft 28 and flywheel 40 must be designed to compensate forthis attraction.

The turbine engine 12 is started by a conventional starter (not shown).Because the first shaft 14 rotates independently of the second shaft 28,the engine 12 may be started easily with a relatively small starter.Only the compressor turbine 16 and the gasifier turbine 18 need torotate to start the engine 12. After the engine 12 is started, exhaustgases from the gasifier turbine 18 are directed to the power turbine 26and begin to spin up the second shaft 28 to normal operating speeds. Thegenerator/motor 30 is mounted concentricity about the second shaft 28and rotates with the power turbine 26. The rotating generator/motor 30creates an AC electric current that is directed to the inverter/powercontroller 32. The mass of the generator/motor 30 and of flywheel 40 maycause the second shaft 28 to rotate at a slower speed than the firstshaft 14 if the size and shape of the gasifier turbine 18 and the powerturbine 26 are comparable. This difference in rotating speed is allowedwithout compromising efficiency because the first and second shafts 14,28 are uncoupled.

Electric current from generator/motor 30 is provided to inverter/powercontroller 32 and then to the electric drive motor/generator 34. Thedrive motor/generator 34 powers wheels 36 and provides motion for thevehicle. When the vehicle undergoes a high load condition such aspassing maneuver or climbing a hill, the additional load required by thedrive motor/generator 34 draws a higher current from inverter/powercontroller 32. This increased load causes an increased torque demand onthe generator/motor 30. The additional torque needed to overcome thetemporary load demanded by drive motor/generator 34 is provided from therotational energy within flywheel 40. As energy is drawn from flywheel40 by generator/motor 30, the speed of the second shaft 28 drops. Whenthe temporary high load condition is relieved, the excess power producedby engine 12 is again directed to increasing the speed of the flywheel40.

When the vehicle is operated in a regenerative braking mode, electriccurrent from the drive motor/generator 34 passes through theinverter/power controller 32 and causes the generator/motor 30 to act asa motor. The generator/motor 30 causes the second shaft 28 and theflywheel 40 to spin faster and stores the excess electric currentproduced by the regenerative braking condition as rotational kineticenergy within flywheel 40. This excess rotational kinetic energy may bereturned to the vehicle in a form of AC electric current throughgenerator/motor 30 operating as a generator.

The vehicle may be operated for short periods of time merely by therotational kinetic energy stored within flywheel 40. Flywheel 40 rotatessecond shaft 28 and causes the generator/motor 30 to produce an ACelectric current. The power turbine 26 also rotates together with secondshaft 28. However, first shaft 14, the gasifier and compressor turbines18, 16 are not rotated.

In the alternative embodiment of the present invention illustrated inFIG. 2, the vacuum containment vessel and magnetic coupling areeliminated. Flywheel 40' is directly connected to an extended secondshaft 28'. This alternative embodiment is less expensive to produce thanthe embodiments shown in FIGS. 1 and 1a because the magnetic couplingand vacuum containment vessel are eliminated. This alternativeembodiment has lower operating efficiency due to the air drag onflywheel 40'. The drag on flywheel 40' lowers the overall operatingefficiency of the vehicle but it also reduces the lost and complexitiesof the hybrid propulsion system 10'.

FIG. 3 illustrates yet another alternative embodiment of the presentinvention which eliminates the need for a magnetic coupling and a vacuumchamber yet does not include the air drag normally associated with afree-standing flywheel. While the engine components described inembodiments illustrated in FIGS. 1, 1a and 2 are commercially available,the power turbine/flywheel assembly 20' illustrated in FIG. 3 is unique.

The embodiment illustrated in FIG. 3 combines the flywheel 40" betweentwo halves of the power turbine. Exhaust gases from the gasifier turbine18 are diverted into two flow paths by a Y-shaped diverter 50. Theexhaust gases spin two turbine blades 52. 54. Flywheel 40" is attachedbetween blades 52, 54 to a second shaft 28'. The turbine blades 52, 54and flywheel 40" spin as a unit. The exhaust gases passing through powerturbine 20' combine in a Y-shaped diverter 66 to form one combined flowpath that leads into the heat exchanger 22.

Illustrated in FIG. 4 is a cross-sectional view of the powerturbine/flywheel assembly 20'. Exhaust gases entering through thediverter 50 are directed into flow paths 56, 58. The flow paths 56, 58receive an approximately equal amount of exhaust gas from the diverter50. Gases from flow path 56 enter turbine blade 52 radially at thelargest diameter of the turbine blade 52. The entering exhaust gases areat a high pressure and temperature. The exhaust gases expand in turbineblade 52 and exit axially through a flow path outlet 62. The gasesexiting the power turbine/flywheel assembly 20' are reduced in pressureand temperature. The expanding exhaust gases from flow path 56 rapidlyrotate the turbine blade 52. Exhaust gases passing through flow path 58rotate the turbine blade 54 and axially exit power turbine/flywheelassembly 20' through a flow path outlet 64. The expanded exhaust gasesfrom the outlets 62, 64 are combined in diverter 66 into one flow path.Exhaust gases passing through outlets 62, 64 are combined in diverter 66and are directed to heat exchanger 22 (not shown in this view). Theoutlet 64 allows the second shaft 28' to pass through a manifold 68.

Positioned between turbine blades 52, 54 is the flywheel 40". Theturbine blades 52,54 and flywheel 40" are all directly attached to thesecond shaft 28' and rotate as a unit. End plates 70, 71 serve tosupport turbine blades 52, 54 and close the ends of the turbine volutesto the flow of exhaust gases. End plates 70, 71 secure turbine blades52, 54 to the axial surfaces 73, 75 of flywheel 40" as shown. Bearings72, 74 serve to support the second shaft 28'.

The aerodynamic drag experienced by the flywheel 40" is believed to beless than that experienced the flywheel 40' as shown in FIG. 2. Theflywheel-to-air contact occurs along a radial surface 76. The axialsurfaces 73, 75 of the flywheel 40" are covered by the plates 70, 71 andare free of aerodynamic drag. The turbine blades 52, 54 and the flywheel40" are contained in a housing 78. Housing 78 has an interior radialportion 79 that closely conforms to the flywheel radial surface 76. Thespace between radial surface 76 and the interior portion 79 isrelatively small in the order of 1 centimeter or less and is chosen tominimize aerodynamic losses. Housing 78 includes apertures 80, 82 thatreceive exhaust gases from flow paths 56, 58. Exhaust gases enteringapertures 80, 82 flow over the radial surface 76. The radial surface 76may optionally include ribs or dimples (not shown) or another surfacetexture to minimize the aerodynamic drag between the exhaust gas and theradial surface 76. The amount of air drag is believed to be minimalbecause the exhaust gas and the radial surface 76 are both moving in thesame direction and at approximately the same speed. While the embodimentillustrated in FIGS. 3 and 4 may not be as efficient as a flywheeltotally enclosed in a vacuum chamber, this embodiment reduces the costand complexity of the overall system by eliminating the need for thevacuum enclosure and magnetic coupling.

While the invention has been illustrated by its preferred embodiments,other embodiments of the present invention are also possible and areintended to be covered within the spirit and scope of the attachedclaims.

What is claimed:
 1. A hybrid electric propulsion system for a vehiclecomprising:an electric drive motor; a generator supplying electriccurrent to said motor; a flywheel; a vacuum containment vessel enclosingsaid flywheel; and a dual shaft turbine engine, said engine having acompressor and a gasifier coupled to a first shaft and a power turbine,said flywheel and said generator coupled to a second shaft, said firstand second shafts being uncoupled and exhaust gases from said gasifiercause said power turbine to rotate, whereby said rotating power turbineturns said generator and flywheel.
 2. The hybrid electric propulsionsystem of claim 1, wherein said flywheel is coupled to said second shaftby a magnetic coupling.
 3. The hybrid electric propulsion system ofclaim 2, wherein said power turbine and said generator rotateconcentrically about said second shaft.
 4. The hybrid electricpropulsion system of claim 3, wherein said second shaft has first andsecond ends, said power turbine is attached to said first end and amagnetic coupling spindle is attached to said second end; and whereinsaid flywheel is attached to and concentrically rotates about a magneticcoupling rotor, said spindle magnetically driving said rotor and turningsaid flywheel.
 5. The hybrid electric propulsion system of claim 4,wherein said generator is attached to said second shaft between saidpower turbine and said magnetic coupling.
 6. A hybrid electricpropulsion system for a vehicle comprising:an electric drivemotor/generator attached to vehicle drive wheels; a generator/motorsupplying and receiving electric current to and from saidmotor/generator; a flywheel; a vacuum containment vessel enclosing saidflywheel; and a dual shaft turbine engine, said engine having acompressor and a gasifier coupled to a first shaft and a power turbine,said flywheel and said generator/motor coupled to a second shaft, saidfirst and second shafts being uncoupled and exhaust gases from saidgasifier turning said power turbine, said turning power turbine turnssaid generator/motor and said flywheel and causes said generator togenerate electric current and operate said motor/generator to rotatesaid drive wheels, and said drive wheels cause said motor/generator togenerate electric current under regenerative braking and operate saidgenerator/motor to rotate said flywheel.
 7. The hybrid electricpropulsion system of claim 6, wherein said flywheel is coupled to saidsecond shaft by a magnetic coupling.
 8. The hybrid electric propulsionsystem of claim 7, wherein said power turbine and said generator rotateconcentricity about said second shaft.
 9. The hybrid electric propulsionsystem of claim 8, wherein said second shaft has first and second ends,said power turbine is attached to said first end and a magnetic couplingspindle is attached to said second end; and wherein said flywheel isattached to and concentricity rotates about a magnetic coupling rotor,said spindle magnetically drives said rotor and turns said flywheel. 10.The hybrid electric propulsion system of claim 9, wherein said generatoris attached to said second shaft between said power turbine and saidmagnetic coupling.
 11. A hybrid electric propulsion system for a vehiclecomprising:an electric drive motor/generator attached to vehicle drivewheels; a generator/motor supplying and receiving electric current toand from said motor/generator; a dual shaft turbine engine, said enginehaving a compressor and a gasifier coupled to a first shaft, and a powerturbine and a generator coupled to a second shaft, said first and secondshafts are uncoupled from each other; a magnetic coupling couples saidsecond shaft to a flywheel, wherein said second shaft, power turbine,generator and flywheel all rotate as a unit, exhaust gases from saidgasifier turn said power turbine and cause said generator to generateelectric current and operate said motor/generator to rotate said drivewheels, and said drive wheels cause said motor/generator to generateelectric current under regenerative braking and operate saidgenerator/motor to rotate said flywheel; and a vacuum enclosuresurrounding said flywheel.
 12. The hybrid electric propulsion system ofclaim 11, wherein said second shaft has first and second ends, saidpower turbine is attached to said first end and a magnetic couplingspindle is attached to said second end; and wherein said flywheel isattached to and concentricity rotates about a magnetic coupling rotor,said spindle magnetically driving said rotor and turning said flywheel.